1. Field of the Invention
The present invention relates to a method of controlling the operation of a condensation reduction system for an exhaust gas recirculation (EGR) system of a compression-ignition internal combustion engine based in part on humidity levels.
2. Background Art
Compression-ignition internal combustion engines may be equipped with EGR systems to reduce NOX emissions. EGR systems include an EGR circuit in which tubing interconnects an EGR cooler, EGR flowmeter, and EGR valve. The EGR circuit components operate in a corrosive environment that is exacerbated by the formation of condensation in the EGR circuit. Gases that condense in the EGR system are acidic and can cause corrosion of the components of the EGR circuit. As exhaust gases cool in the EGR circuit, condensation may form on the interior surfaces of the components of the EGR circuit.
Various condensation reduction or elimination systems are available for use on internal combustion engines including condensation traps, EGR heaters, and the like. Control and operation of active systems may require energy and control logic capacity. Under most normal operating conditions no condensation reduction system is necessary, but prior art systems continuously function regardless of ambient temperature and humidity conditions.
There is a need to eliminate or reduce condensation in EGR systems selectively when ambient temperature and humidity conditions cause condensation to prolong the life of the EGR circuit components by minimizing corrosion. There is a need for a method and apparatus for minimizing operation of condensation reduction systems in an EGR circuit when ambient temperature and humidity conditions do not necessitate condensation reduction.
The above problems and needs are addressed by Applicant""s invention as summarized below.
According to one aspect of the present invention, a method of controlling an internal combustion engine is provided wherein humidity is used to control operation of a system for reducing condensation in the EGR system. The system includes an exhaust gas recirculation system for an exhaust gas mixed with intake air that is provided to the intake manifold. The humidity of the intake gas is measured and compared to a predetermined value. The system for reducing condensation in the EGR system is controlled based upon the comparison of the measured humidity and the predetermined value.
According to other aspects of the invention, humidity may be measured in the intake manifold of the engine or in the mixing chamber upstream from the intake manifold where the exhaust gases are mixed with intake air.
According to another aspect of the invention, the step of comparing the humidity of the intake gases may further comprise determining whether the temperature of the intake gases are above the dew point. The determination of the dew point of the intake gas may be based upon the calculation of different levels of humidity at different ambient temperatures at a given speed and load of the engine. The calculation of different levels of humidity may rely upon data indicative of the intake manifold pressure, EGR flow, and air/fuel ratio. The temperature of the mixture gases in the intake manifold (IMT) and the dew point of the mixture (IMTc) may be compared so that the EGR is shut off when the IMT is less than IMTc.
According to another aspect of the invention, an exhaust gas recirculation system for a compression ignition engine has a condensation monitoring system. The condensation monitoring system includes a humidity sensor that is included as part of the control circuit. The humidity sensor determines when conditions in the intake manifold are conducive to the formation of condensation. The control circuit stops the EGR system when it is determined that conditions in the intake manifold are conducive to the formation of condensation.
According to other aspects of the EGR system of the present invention, the humidity sensor may be disposed in the intake manifold. Alternatively, the humidity sensor may be disposed in the mixture pipe into which the EGR system provides exhaust gases and a charge air cooler provides intake air.
A further alternative is to locate the humidity sensor to sense ambient humidity.
According to another aspect of the invention, an intake manifold pressure sensor, an EGR flowmeter and a system for determining the air/fuel ratio may be used by the control circuit to calculate the dew point of the mixture of gases in the intake manifold. The calculations may be for a given speed and load for different levels of humidity at different ambient temperatures based upon data received from the intake manifold pressure sensor, the EGR flowmeter and the system for determining the air/fuel ratio.
According to yet another aspect of the invention, the temperature of the mixture of gases in the intake manifold may be designated IMT and the dew point of the mixture may be represented as IMTcwith the EGR being shut off when IMT is less than IMTc.
The above advantages, and other advantages, objects, and features of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.